NEW MATERIAL:The compound of formula I (R1 is H, halogen or hydrocarbon group; R2 and R3 are H or hydrocarbon group; one of m and n is 1 and the other is 0; either one of the groups of formula II is single bond and the other is double bond according to the value of m and n).

EXAMPLE: 3-Phenyl-6-trifluoromethyl-1,2,4-triazin-5(2H)-one.

USE: Pharmaceuticals, agricultural chemicals or their intermediates.

PREPARATION: The compound of formula I or formula III wherein R2 and R3 are H can be produced by reacting amidrazones of formula II with hexafluoropropylene oxide in a solvent such as ethanol. Substitution of the product with hydrocarbon group gives another compound of formula I or III wherein R2 and R3 are hydrocarbon group. As an alternative method, the compound of formula I or formula III can be produced by reacting a compound of formula IV with a trifluoropyruvic acids of formula V (R5 is hydrocarbon group) or its hydrate.